Pretensioning system



March 1953 'w. D. VAN ZE'LM ET AL 2,827,248

PRETENSIONING SYSTEM Filed April 9, 1956 INVENTORS W/LLEM D. VAN ZELM K/RKWOOD 5. NEW, JR.

ATTORNEYS United States Patent PRETENSIONING SYSTEM Willem D. van Zelm, Ruxton, and Kirkwood S. Nevin, Jr., White Hall, Md., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application April 9, 1956, Serial No. 577,183

2 Claims. (Cl. 244-63) The present invention relates to a pretensioning system for catapults. More particularly the invention relates to a pretensioning system' for pressure operated launching devices wherein excessive acceleration forces present in devices of the prior art are prevented in the driving sys tem of the present invention. In order to accomplish the foregoing a pretensioning cylinder is provided to maintain a predetermined pressure on one of the sheaves over which the driving strap of the launching device passes.

An object of the present invention is to provide a pretensioning apparatus for pressure operated launching devices wherein excessive forces on the driving apparatus are avoided.

Another object is to provide a pretensioning apparatus wherein the initial high accelerating force in the drive mechanism of a catapult is controlled to prevent overloading of the drive mechanism.

A further object is to provide pretensioning apparatus for catapults which is simple in construction, efficient in operation, and durable in service.

Other objects and many of the attendant advantages of this invention will 'be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. l is a diagrammatic view of a catapult apparatus according to the invention and showing the components in an initial or unoperated position;

Fig. 2 is a view similar to Fig. 1 and showing the components in an accelerating position; and

Fig. 3 is a similar view showing the components in a braking position at the end of the launching operation.

Referring more particularly to the drawings wherein like numerals indicate like parts throughout the several views, indicates a sheave rotatably mounted on a fixed support 11. sheave 10 is a sheave 12, which is mounted on support 13 for rotation thereon and for linear motion therewith. Support 13 passes through one end of a pretensioning cylinder 14 and has a piston 15 fixed to the end within the cylinder.

An endless belt or strap 16 passes over the sheaves 1i) and 12 and has secured thereto on the upper run a launching car 17 which is adapted to engage an aerodynamic body such, for example, as a target drone or the like. The lower run of strap 16 has secured thereto a driving piston 18 which is enclosed in an elongated driving cylinder 19 fixedly positioned between the sheaves 10 and 12.

Cylinder 19 may be fitted at the ends thereof with means (not shown) for preventing leakage between the cylinder end walls and strap 16. Cylinder 19 is connected at one end by a conduit 21 with a source of pressure 22. A valve 23 is connected in conduit 21 whereby cylinder 19 may be connected to or shut off from the source of pressure 22.

The opposite end of cylinder 19 is provided with a pressure equalizing chamber 24 containing a length of Spaced a substantial distance from w 2,827,248 Patented Mar. 18, 1958 hereinafter more fully described. A conduit 26 connects pretensioning cylinder 14 with the pressure source 22.

It is apparent from the drawings that the pretensioning cylinder 14 is connected directly to the source of pressure 22 by the conduit 26 and therefore is charged to the pressure of the source 22 at all times. Assuming that the area of piston 15 is 2.2 times the area of piston 18 and is subjected to the same pressure, the load in each half (the upper and lower runs) of strap 16 is 1.11 (where P is the required launching load or is equal to the area of the piston 18 times the pressure in source 22), then the load on the piston 15 is 2.2P. This condition prevails when the apparatus is in the initial or unoperated position, as shown in Fig. 1.

In Fig. 2, the valve 23 having been actuated, the ac celerating phase of operation of the device is initiated. Opening valve 23 causes fluid under pressure to pass through conduit 21 from the source of pressure 22 and into cylinder 19 thus toengage piston 18. Therefore, both cylinder 14 and cylinder 19 operate at the same pressure but the force on piston 15 is always 2.2 times the force on piston 13 due to the difference in area. The force P on piston 18 tends to increase the load on a drive circuit which includes that part of strap 16 which passes from the piston 18, over sheave 12 and to the launching car 17. Piston 15 can only support a maximum of 2.21 and thus cannot support the aforementioned additional load transmitted thereto from strap 16 through sheave 12 and support 13, and therefore moves slightly into pretensioning cylinder 14. The foregoing permits the piston 18 to move slightly in a direction to relieve the pretensioning load in that part of the drive system around the sheave 10. This action continues until all forces are in equilibrium, whereupon the force P on piston 18 is applied through strap 16 to the launching car 17. The load in the drive circuit remains the same as in the initial position, l.lP, while the load on that part of the strap 16 leading from the piston 18, over sheave 10 and on to ca1117 is reduced to 0.1? as its load is: caused by the elastic stretch of the strap under the pretension load. The residual load of (HP in the strap 16, from piston 18 around sheave 10 to car 17, is the resultant force which equalizes the forces in strap 16 when the maximum load of 2.21 of piston 15 is overcome by the addition of the firing load P applied by piston 18 to the drive circuit, moving the piston 15 into cylinder 14. Thus it will be seen that the accelerating force P is applied to the car 17 not by increasing the load in the upper half of the strap, from piston 18 over sheave 12 to car 17, but by reducing the pretension load in the lower half of the strap 16 running from the piston 18 over sheave 10 to car 17. in this way the pretensioning piston acts as a load limiting means by preventing loads in excess of l.lP on the drive strap.

The pretension load in the strap 16 may be made any desired value merely by selecting the ratio of the diameter of the piston 15 to the piston 18. The value of the ratio chosen for illustration purposes (2.2:1) specifies a practical lower limit of pretension load (0.1P) in the lower half of the strap 16 so it will never go slack.

As the piston 18 approaches the end of its movement, it enters the tubing 25 in equalizing chamber 24, whereupon the fluid under pressure passes into chamber 24 and around tubing 25 to enter the opposite end thereof, thus equalizing the pressure on both sides of the piston to relieve the piston of its propelling force and to stop the piston prior to reaching the end of the tube 19. This braking phase of the operation is shown in Fig. 3.

The return of the piston 18 to the initial position may be accomplished in any desired manner and forms no part of the present invention.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A pretensioning apparatus for catapults comprising, a pair of spaced sheaves, one of said sheaves being fixed against linear movement, the other of said sheaves being linearly movable, an endless strap passing over said sheaves and having an upper run and a lower run, a driving cylinder fixedly mounted between said sheaves, the lower run of said strap passing through said cylinder, a driving piston fixedly mounted on said strap and mounted for linear movement in said driving cylinder, a source of fluid under pressure, a conduit connecting said source with one end of said cylinder, valve means in said conduit for permitting said fluid under pressure to flow into said driving cylinder to drive said strap and operate said catapult, a pretensioning cylinder, means connectingsaid pretensioning cylinder with said source whereby the pres sure in said pretensioning cylinder is maintained at the same value as the pressure of said source, a pretensioning piston mounted for axial motion in said pretensioning cylinder, said pretensioning piston having a greater area than said driving piston and means connecting said pretensioning piston with said other sheave for yieldably resisting linear motion of said other sheave.

2. Pretensioning apparatus for a pressure operated belt drive catapult comprising a fixed sheave and a linearly movable sheave, a source of fluid maintained under predetermined pressure for operating said catapult, a driving cylinder fluid connectable with said source, a driving piston mounted for linear movement in said cylinder; said driving piston being operatively connected to said belt, a tensioning cylinder connected to said source of fluid, a tensioning piston movably mounted in said tensioning cylinder and receiving said predetermined pressure, said tensioning piston having a diameter more than two times the diameter of said driving piston, and means connecting said linearly movable sheave with said tensioning piston whereby the predetermined pressure of said fluid resists linear movement of said movable sheave.

References Cited in the file of this patent UNITED STATES PATENTS 1,347,105 Mesurier July 20',- 1 920 FOREIGN PATENTS 7 358,763 Italy Apr. 29, 1938 480,692 Great Britain Feb; 25, 1938' 

